A Cr(iii) supramolecular network composite membrane with high water stability and proton conductivity

Abstract

Proton exchange membranes have attracted considerable attention as the core component of fuel cells. Among them, the blending matrix membrane will result in a composite membrane with the advantages of individual components. Chitosan (CS) has a strong binding capacity to Cr³⁺ ions, and it combines with polyvinylpyrrolidone (PVP) to form a rich network of hydrogen bonds. Hence, the composite membrane of blending hydrophilic polymer CS-PVP matrix and metal-hydrogen-organic frameworks (MHOFs) [Cr₂(DBPZ)₂(μ-OH)₂] 1 (H₂DBPZ) = bis(3,5-dicarboxypyrazol-1-yl)dicarboxylic acid were fabricated. The Cr³⁺ ion is six-coordinated by four oxygen atoms and two nitrogen atoms to form an octahedron configuration. Two DBPZ²⁻ ligands connected two Cr³⁺ ions forming a dimeric unit, and an adjacent dimeric core are further connected by a hydrogen bond to form a 3D supramolecular framework. The proton conductivity of 1@CS/PVP-10 reached up to 8.64 × 10⁻² S cm⁻¹ at 363 K and 98% RH, which is about 10 times higher than that of 1.